The present invention relates to a slip sheet insertion-delivery apparatus for inserting and delivering a slip sheet between adjacent printing sheets in order to prevent offsetting when sheets are delivered and stacked in a sheet-fed printing press.
In a sheet-fed printing press, a sheet conveyed by a delivery chain after printing is released at a rear end of a conveying path and is dropped and stacked on a stack board. However, ink on a sheet immediately after printing is not yet dried, and if such sheets are stacked in this state, offsetting occurs. In order to prevent this, in a conventional printing press, powder is sprayed on a printed surface between a printing apparatus and a delivery apparatus or a printed surface is dried upon radiation of an infrared ray.
However, like in intaglio printing, a thickness of an ink film on a printed surface reaches several tens of microns, i.e., about ten times that in a lithographic printing press. In this case, even through a printed surface is forcibly dried by an infrared ray, drying is not sufficient. If powder is sprayed on a printed surface, quality of a printed product is degraded. Therefore, a slip sheet insertion-delivery apparatus which inserts a slip sheet between adjacent printing sheets when the sheets are delivered on a stack board has been conventionally used.
FIGS. 6 and 7 show a conventional slip sheet insertion-delivery apparatus. In FIGS. 6 and 7, a plurality of pairs of right and left gripper rod holders 2 are disposed at predetermined intervals between a pair of right and left delivery chains 1 which travel while circulating between a printing apparatus and a delivery apparatus. A gripper rod 6 consisting of a stationary gripper pad shaft 3, a pivotal printing sheet gripper shaft 4 and a pivotal slip sheet gripper shaft 5 is axially supported between each pair of right and left gripper rod holders 2. A plurality of gripper pads 7 are parallelly split-fixed on the gripper pad shaft 3. A plurality of printing sheet grippers 8 and slip sheet grippers 9 are parallelly split-fixed to the gripper shafts 4 and 5, respectively, to have different phases from those of the gripper pads 7. Cam levers 12 and 13 on which cam followers 10 and 11 are pivotally mounted on their free end portions, respectively, are axially mounted on the shaft end portions of the gripper shafts 4 and 5. Upon traveling of the delivery chains 1, the cam followers 10 and 11 face cams provided near a printing cylinder on the side of a frame at a delivery position, so as to open the grippers at a predetermined timing.
With the above arrangement, when the delivery chains 1 travel and the cam follower 10 is in contact with the cam near the printing cylinder, only the printing sheet grippers 8 are opened and closed to regrip the printing sheet from the grippers of the printing cylinder. Then, the sheet is conveyed to be gripped by the printing sheet grippers 8 and the gripper pads 7. Upon regripping, since the slip sheet grippers 9 are kept closed, a sheet 14 is gripped by the printing sheet grippers 8 to cover the slip sheet grippers 9, as shown in FIG. 8. When the gripped edge of the sheet 14 conveyed in this manner has reached the front of the stack board, a slip sheet is fed onto a feeder board, and the cam follower 11 faces the corresponding cam, so that the slip sheet grippers 9 are opened and closed while causing the printing sheet 14 to leap up, and grip the slip sheet between themselves and the gripper pads 7. Thereafter, when the slip sheet has reached the stack board, the grippers 8 and 9 are simultaneously opened to deliver the printing sheet 14 and the slip sheet to overlap each other.
However, in the conventional slip sheet insertion-delivery apparatus, since each pair of the gripper rods 6 include the two gripper shafts 4 and 5 for the printing sheet and the slip sheet, the overall traveling mechanism including the gripper rod holders 2 is heavy, thus interfering with high-speed and smooth operation. As described above, the printing sheet 14 covers the slip sheet grippers 9, as shown in FIG. 8. When the slip sheet is gripped, the slip sheet grippers 9 must be opened while causing the printing sheet 14 to leap up, and the printing sheet 14 can be easily torn. In order to prevent this, a pitch indicated by p in FIG. 8 between the grippers 8 and 9 must be increased or a gripping margin of the slip sheet gripper indicated by t in FIG. 7 must be decreased. Therefore, paper sheets may be wasted due to misgripping. Thus, the operation is unstable, and adjustment is not easy.